Method for measuring a speed of a fluid

Abstract

A method of measuring the speed of a fluid comprising the following steps:generating a plurality of pseudorandom frequencies (fus_n);for each pseudorandom frequency (fus_n), emitting ultrasound signals into the fluid to travel along a path of defined length;receiving the ultrasound signals;for each received ultrasound signal, producing a travel time measurement, so as to generate for each pseudorandom frequency (fus_n) a predefined number of travel time measurements;for each pseudorandom frequency (fus_n), evaluating the accuracy of the measurements;for evaluating the speed of the fluid, making use of the measurements produced for the pseudorandom frequency that presents the greatest accuracy.

The invention claimed is: 
     
       1. A method of measuring the speed of a fluid, the method comprising:
 measurement stages, each comprising the following steps:
 generating a plurality of pseudorandom emission frequencies (fus_n); 
 for each pseudorandom emission frequency (fus_n), producing travel time measurements representative of times taken by ultrasound measurement signals emitted at said pseudorandom emission frequency to travel along a path of defined length; 
 for each pseudorandom emission frequency (fus_n), evaluating the accuracy of the travel time measurements; and 
 for evaluating the speed of the fluid, making use of the travel time measurements produced for the pseudorandom emission frequency (fus_k) that presents the greatest accuracy; 
 and 
 
 detection stages, each performed between two measurement stages, each detection stage comprising the following steps:
 measuring an interfering ultrasound signal level present in the fluid; 
 comparing the interfering ultrasound signal level with a current value of a detection threshold, the detection threshold being capable of taking a plurality of predefined values lying between a maximum detection threshold and a minimum detection threshold; 
 if the measured interfering ultrasound signal level is less than the current value of the detection threshold, reducing the current value of the detection threshold, and reiterating the measurement step and the comparison step; and 
 when the measured interfering ultrasound signal level becomes greater than or equal to a limit current value of the detection threshold, detecting a disturbance and, as a function of the limit current value of the detection threshold, determining whether the disturbance comes from an anomaly or from an attempted fraud. 
 
 
     
     
       2. The measurement method according to  claim 1 , wherein each of the the measurement stages further comprising, for each pseudorandom emission frequency (fus_n), evaluating the accuracy of the travel time measurements comprises a step of calculating a mean M′ fus_n  of the travel time measurements, and a step of determining a number of inaccurate travel time measurements lying outside a range [M′ fus_n −X, M′ fus_n +X], the emission frequency that presents the greatest accuracy being the frequency for which the number of inaccurate travel time measurements is the lowest,
 wherein for a received ultrasound measurement signal, the travel time measurement is obtained on the basis of determining a moment of arrival for a predetermined lobe of the received ultrasound measurement signal. 
 
     
     
       3. The measurement method according to  claim 2 , wherein X lies in the range 3% to 30% of M′ fus_n . 
     
     
       4. The measurement method according to  claim 2 , wherein a mean travel time used for evaluating the speed of the fluid is equal to the mean M fus_k  of the travel time measurements within the range [M′ fus_k −X, M′ fus_k +X], fus_k being the emission frequency that presents the greatest accuracy. 
     
     
       5. The measurement method according to  claim 2 , wherein the moment of arrival is the instant at which a rising front of the predetermined lobe arrives. 
     
     
       6. The measurement method according to  claim 2 , wherein the predetermined lobe is a j th  lobe of the received ultrasound measurement signal after the received ultrasound measurement signal presents an amplitude that exceeds a predetermined amplitude threshold. 
     
     
       7. The measurement method according to  claim 1 , wherein the plurality of pseudorandom emission frequencies (fus_n) are generated by making use of a cycle counter of a microcontroller. 
     
     
       8. The measurement method according to  claim 1 , wherein the plurality of pseudorandom emission frequencies (fus_n) are generated by making use of a generator polynomial. 
     
     
       9. The measurement method according to  claim 1 , wherein the pseudorandom emission frequencies (fus_n) lie in the range 900 kHz to 4 MHz. 
     
     
       10. The measurement method according to  claim 1 , wherein the pseudorandom emission frequencies (fus_n) are spaced apart from one another by at least a predefined frequency difference. 
     
     
       11. The measurement method according to  claim 10 , wherein the predefined frequency difference lies in the range 5 kHz to 50 kHz. 
     
     
       12. The measurement method according to  claim 1 , wherein each of the predefined values of the detection threshold is referenced by an index presenting values that decrease with increasing index, and wherein a disturbance is determined as coming from an anomaly if the index of the limit current value of the detection threshold is greater than a predefined index threshold, and a disturbance is determined as coming from an attempted fraud if the index of the limit current value of the detection threshold is less than or equal to the predefined index threshold. 
     
     
       13. The measurement method according to  claim 12 , wherein the predefined index threshold is adjustable. 
     
     
       14. The measurement method according to  claim 13 , wherein the predefined index threshold is adjustable as a function of the time of day at which the detection stage is performed. 
     
     
       15. The measurement method according to  claim 1 , wherein the detection stage also includes a waiting step for delaying performance of the measurement step by a predefined delay time. 
     
     
       16. The measurement method according to  claim 15 , wherein the predefined delay time is measured on the basis of a moment when the level of the ultrasound measurement signal generated during a preceding measurement stage has become lower than a predetermined silence threshold. 
     
     
       17. The measurement method according to  claim 1 , wherein the detection stage also includes steps of emitting a decoy ultrasound signal, and of attempting to detect a fraudulent ultrasound signal emitted in response to the decoy ultrasound signal. 
     
     
       18. The measurement method according to  claim 1 , wherein the detection stage also includes the step of transmitting the measured level of the interfering ultrasound signal to external equipment. 
     
     
       19. The measurement method according to  claim 18 , wherein the measurement stages and the measurement step in each detection stage are performed in an ultrasound fluid meter, and wherein the steps following the measurement step of each detection stage are performed in the external equipment. 
     
     
       20. The measurement method according to  claim 18 , wherein the external equipment is a server in the “cloud”. 
     
     
       21. The measurement method according to  claim 1 , wherein the detection stage also includes the step of transmitting a warning message when a disturbance is detected. 
     
     
       22. The measurement method according to  claim 21 , wherein the warning message is transmitted by powerline carrier. 
     
     
       23. An ultrasound fluid meter comprising a first transducer, a second transducer, and processor means arranged to perform the measurement method according to  claim 1 . 
     
     
       24. A computer program including instructions for enabling an ultrasound fluid meter to perform the measurement method according to  claim 1 . 
     
     
       25. Storage means wherein they store a computer program including instructions for enabling an ultrasound fluid meter to perform the measurement method according to  claim 1 . 
     
     
       26. A method of measuring the speed of a fluid, the method comprising measurement stages, each comprising the following steps:
 generating a plurality of pseudorandom emission frequencies (fus_n); 
 for each pseudorandom emission frequency (fus_n), producing travel time measurements representative of times taken by ultrasound measurement signals emitted at said pseudorandom emission frequency to travel along a path of defined length; 
 for each pseudorandom emission frequency (fus_n), evaluating the accuracy of the travel time measurements; 
 for evaluating the speed of the fluid, making use of the travel time measurements produced for the pseudorandom emission frequency (fus_k) that presents the greatest accuracy; 
 the measurement method being such that, for each pseudorandom emission frequency (fus_n), evaluating the accuracy of the travel time measurements comprises a step of calculating a mean M′fus_n of the travel time measurements, and a step of determining a number of inaccurate travel time measurements lying outside a range [M′ fus_n −X, M′ fus_n +X], the emission frequency that presents the greatest accuracy being the frequency for which the number of inaccurate travel time measurements is the lowest, 
 wherein the measurement method further comprises detection stages, each performed between two measurement stages, each detection stage comprising the following steps:
 measuring an interfering ultrasound signal level present in the fluid; 
 comparing the interfering ultrasound signal level with a current value of a detection threshold, the detection threshold being capable of taking a plurality of predefined values lying between a maximum detection threshold and a minimum detection threshold; 
 if the measured interfering ultrasound signal level is less than the current value of the detection threshold, reducing the current value of the detection threshold, and reiterating the measurement step and the comparison step; 
 when the measured interfering ultrasound signal level becomes greater than or equal to a limit current value of the detection threshold, detecting a disturbance and, as a function of the limit current value of the detection threshold, determining whether the disturbance comes from an anomaly or from an attempted fraud.